Like most of South America it isn't great for Tier Point Runs because there is no longer a Oneworld member airline in South America. Assuming you are coming from the UK you might be better off building a normal ex-Europe flight to the West Coast, then staying there overnight and then booking a separate return fair via Miami to Santiago.

Basically if you look at FlightConnections.com - there's only 6 routes for One World airlines into Santiago - DFW and Miami with American, BA from London and Iberia from Madrid and Barcelona and Sydney with Qantas. Most of these are way too long for Tier Points purposes.

If you do a normal West Coast run from Europe and then do LAX-MIA-Santiago return then you'll get the normal points for the run plus 280 tier points each way. I have no idea how the pricing of all this works though - it might not be practical at all. You could look at other destinations in South America and then connect onwards using someone else to Santiago. Or even conceivably a Oneworld around-the-world flight might be cheaper...